Furuno CSH-5L Operator's Manual page 81

8. MAINTENANCE, TROUBLESHOOTING
SIO test
This test checks the input/output ports (CN-A1, NMEA1/CIF1, NMEA2/CIF2) of
the processor unit. The result for the CN-A1 port is shown as OK or NG (No
Good).
The test for the NMEA1/CIF1 and NMEA2/CIF2 ports is for factory use. The
result is always NG.
SIO test
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